Cellular function is regulated, in part, by the precise location and concentration of ions. The asymmetrical distribution and movement of ions across intra-and extracellular membranes are responsible for producing electrical responses that control the physiological state of the tissue. Secondary Ion Mass Spectrometry (SIMS) is one of few techniques which permit simultaneous elemental localization and elemental quantitation. The broad objectives of this proposal are to study the role of sodium, potassium, calcium and barium in selected areas of ocular physiology using SIMS. The location and concentration of these ions in photoreceptor outer segments (ROS), intercellular matrix and retinal pigment epithelial (RPE) cells will be determined as a function of dark and light adaptation. These studies will measure directly ion movements associated with light induced cellular activity such as the ROS membrane potential and photomechanical movement of pigment and photoreceptors in vertebrates. Ion gradients across RPE cells will be measured directly. The routes, location and concentration of ion fluxes in normal lens galactose-induced cataract and in reversal of cataractogenesis will be determined. The biochemical processes associated with these ion movements will be studied by analysis of proteins associated with control of ion transport, such as calmodulin (CaM). The feasibility studies of the previous grant period will be extended to determine if SIMS can be used to directly image stable and/or radioactivity labelled to develop quantitative image processing and cold transfer stage capabilities in order to perform quantitative analysis of problems of ROS-RPE interactions described above.